Musical electronic instrument keying with direct current of plural musical effects

ABSTRACT

An electronic musical instrument is provided with a DC current switching circuit for controlling gates that are disposed between various sources of AC potential of audio signal frequency and conventional voicing circuits and signal-to-sound converting means. The switching circuit is under the control of key switches, voice tab switches, preset voice switches, percussion switches, and repeat switches respectively associated with appropriate circuitry to provide one composite DC keying circuit.

United States Patent Inventor Peter T. Savon Glenview, I11.

June 25, 1970 Dec. 14, 197 l v Chicago Musical Instrument Co.

Llncolnwood, Ill.

Appl. .No. Filed Patented Assignee MUSICAL ELECTRONIC INSTRUMENT KEYING WITH DIRECT CURRENT 0F PLURAL MUSICAL EFFECTS 35 Claims, 6 Drawing Figs.

US. Cl 84/L01, 84/103, 84/1 .26, 84/D1G. 23

Int. Cl G10h l/02 Field of Search 84/1 .03, 1.13, 1126, DIG. 23, 1.01

References Cited UNITED STATES PATENTS 12/1970 Freeman 1/1971 Freeman 2/1971 Bunger 1 I a7 1 :(owu/AQ 1' I I E l I Primary Examiner-D. F. Duggan Assistant ExaminerStan1ey .1. Witkowski Attorney-Hill, Sherman, Meroni, Gross and Simpson ABSTRACT: An electronic musical instrument is provided with a DC current switching circuit for controlling gates that are disposed between various sources of AC potential of audio signal frequencyand conventional voicing circuits and signalto-sound converting means. The switching circuit is under the control of key switches, voice tab switches, .preset voice switches, percussion switches, and repeat switches respectively associated with appropriate circuitry to provide one composite DC keying circuit.

I 27 I #40 I I I I I I 1' -T: I

27 I 29 I /6b I I l I L' J I I 7 I 2 I ylC I I I I I (J I I I I I 474m I L 1 1) PATENTED DEC 1 4 l97l SHEET 2 BF 5 INVI'JN'I rm pfTEK T Sm/OA/ MUSICAL ELECTRONIC INSTRUMENT KEYING WITH DIRECT CURRENT OF PLURAL MUSICAL EFFECTS BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to musical instruments and more specifically to a unified DC-circuit under the control of key switches and various tab switches for gating selected combinations of electrical tone signals.

2. Prior Art Heretofore, it has been necessary to provide a considerable amount of switching in order to perform two functions. For instance, prior art devices employ conventional generators or tone signal sources to produce conventional tones and in addition employ separate generators or tone signal sources to produce tones that have a percussive envelope. In such structure, if separate generators were not employed, a very predominant or noticeable blank might result, for instance if the desired generator were already on or coupled.

Heretofore, switching circuits have been complex, both physically and electrically.

Heretofore, electronic presets have been provided which are connected to formant circuits. For instance, a preset that couples flute signals to the formant circuit that employs continuous tones, and another preset that couples flute signals to a second formant circuit for percussive-envelope tones.

Further, prior sustain circuits which rely on a capacitor discharge to provide the decay or delay are constructed to "look into", that is to act on, a substantially fixed impedance, because if such impedance varied, the duration of the decay would vary from note to note or chord to chord.

Heretofore, where there has been considerable borrowing, namely the use of a single signal source under the command of various keys, then when both such keys are depressed, unlike a pipe organ, it could be that additional signal or sound would not be obtained.

SUMMARY OF THE INVENTION In this invention, a switching circuit is provided that can be used to switch or to control the keying of various types and sizes of electronic instruments. In this invention, voice-tab switches are used to control gates in the keying circuit between the keyed source of potential and the point controlled thereby to effect signal read out. To this end, a DC- keying signal is under the control of a key switch, and the keying signal passes through an input resistor to a voltage-controlled gate. A control resistor is also connected between a tab switch and the gate for regulating the ability of the key switch to open the gate.

Accordingly, it is an object of the present invention to provide a unified switching system for controlling DC-keying potential.

Another object of the present invention is to simplify existing circuits, both physically and electrically, for the purpose of cost reduction.

Another object of the present invention is to provide electronic presets that are connected to a switching matrix whereby a single formant circuit is employed for both continuous tones and for percussive-envelope tones, thereby eliminating the prior switching that has been used to select continuous tone formant circuits or percussive-envelope tone formant cir. cuits.

A still further object of the present invention is to provide a keying circuit whereby when one signal source is keyed through the closing of one key switch, and the same signal source is keyed by means of another key switch, additional signal will be read out from the same signal source so that something is actually added to the tone signal that is first being read out.

Yet another object of the present invention is to fulfill the preceding object no matter whether both signals are sustained notes in the sense of being continuously on or whether either or both of them has a percussive envelope.

Another object of the present invention is to provide a keying circuit wherein two tone signal sources are controlled by thesame key switch, but wherein independent tab switches are provided for the two tone signal sources.

The keying circuits or matrix of this invention are so constructed as a network that depending, for example, on how many keys are simultaneously depressed. the total impedance thereof will vary a good deal. Accordingly, it is a further object to provide a sustain circuit section for DC-keying as a part of this invention that will not be affected by such variable impedance and hence provide the same delay for any selected combination of keys and voices.

The term key switch as used herein refers to an electrical switch that is physically actuated as a consequence of the normal playing of the instrument.-

THe term tab switch? is used herein not as a form of construction, but to identify manual selector switches that are used for the selection of voicing, musical effects and the like as distinguished from those identified with a chromatic keyboard. Thus, this term refers to electrical control switches generally found on instruments such as organs and the term is not restricted to internally hinged tabs, rocker buttons, slide bars or any other physical form.

The terms percussion", percussive voice and percussive envelope are all used herein as referring to musical tones that have a distinctive attack coupled with a musical pitch, such as bells, triangles, Xylophone, marimba, piano and tympani, and not mere noise sources that may be used in the percussion section of an orchestra such as bass drums, wood blocks, snare drums, cymbals etc.

Many other advantages, features and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheetsof drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.

ON THE DRAWINGS:

FIG. Us a diagrammatic view of an electronic musical instrument having a unified DC-keying circuit connected between audio signal sources and voicing circuits in accordance with the principles of the present invention.

FIG. 2 is a schematic diagram of a portion of FIG. I including further detail;

FIG. 3 is a circuit diagram of a portion of the circuit shown in FIGS. 1 and 2;

FIG. 4, comprising FIGS. 40 and 4b which are to be viewed side by side, is a schematic diagram showing further detail of the switching circuit of FIG. 1 including representative portions thereof; and

FIG. 5 is a further schematic diagram of certain coacting portions of the keying circuit of FIG. 1.

AS SHOWN ON THE DRAWINGS:

The principles of the present invention are particularly useful when embodied in an electronic musical instrument such as shown in FIG. 1, generally indicated by the numeral 10. The circuit of the instrument 10 includes a set of key switches 11 which control a DC-keying circuit which in turn controls a set of audio signal sources I2 for coupling such signals to conventional voicing or formant circuits 13, the output of which is delivered to an audio amplifier 14 for driving one or more speakers 15. TI-Ie DC-switching circuit includes a matrix 16 through which the key switches 11 act, and such action is under the control of a set of voice tab switches I7. If desired, a set of presets 18 may be provided to operate in lieu of or together with the voice tab switches 17. A percussion circuit 19 is under the control of a set of percussion tab switches 20 and includes a detector 21 for sensing each actuation of one of the key switches 11 to initiate percussion control of the matrix 16. The percussion circuit 19 may act directly on the matrix 16, and is also connected to override momentarily and automatically any control that may then be provided by any of the voice tab switches 17 or the presets 18. A repeat circuit 22 is also connected to control the matrix 16 and its function is controlled by repeat switches which may be combined with the percussion tab switches 20. The repeat signal can be transmitted directly to the matrix 16, and can also be sent to the percussion circuit 19 for control thereof. If desired, and preferably, there are provided sustain keyers 23 for each of the key switches 11, and when the sustain keyers 23 are off there is in effect a direct connection between the key switches 11 and the matrix 16.

There is a key switch 1 l for every key on the instrument and each such key has a sustain keyer 23. All the sustain keyers 23 are under the control of one or more sustain tab switches 24. There are as many voice tab switches 17 provided as there are voices desired for a particular instrument. There are as many presets 18 provided as may be desired in a particular instrument. There are as many percussion and repeat tab switches provided as there are ranks. (In pipe organ terminology, there are various physical ranks of pipes, each rank taking as identification the length of the longest pipe, and therefore analogous nomenclature is used herein). As explained below, in this embodiment, there are eight percussion and repeat tab switches 20.

In addition, the key switches 11 are provided with a number of control tab switches 25 for controlling attack, for turning the percussion circuit 19 on and of? and for turning both the percussion circuit 19 and the repeat circuit 22 on" and off".

For the production of conventional continuous tones, the key switches 11 directlycontrol the matrix 16 under the control of the voice tab switches 17 for gating the audio signal sources 12 to the voicing circuits 13. Such portion of the instrument is shown in FIG. 2, each of the switches such as 110, 1 lb and 110 being arranged to bring a keying potential such as B+ to a number of matrix units l6a-j. Each key switch 11 has such number of matrix units as correspond to the total number of all of the times that the various tab switches for different voices are to use that particular key. Thus, if there are eight tab switches which are to be associated with a particular key switch 11, then there are eight such matrix units provided for such tab switch. FOr the sake of simplicity, FIG. 2 merely illustrates three representative key switches 11 and each one is merely provided with three matrix units such as l6a-c which are controlled by three tab switches 17a-c. In this example, there has been included only three audio signal sources 12a-c, each controlled by a gate 26 connecting it to one of the voicing circuits 13ac. The tab switch 17a is associated wit the matrix 160, 16f and 16] for controlling them simultaneously. With the tab switch 17a closed, the key switches 11a and 11b are enabled to gate the signal sources 12a and 12b. With the tab switch 17b closed, the key switch 11a is enabled to gate the signal source 12b which typically is an octave higher than the signal source 120, and the key switch 11b is enabled to gate the signal source 12c, which is an octave above the signal source 12b. When the tab switch 170 is closed, the key switches Ila-c can only key signal sources 12 that have been omitted from this abridged drawing. When a tab switch 17 is open, the keying potential that is provided by each of the key switches 11 is blocked by the associated matrix units 16a, etc. When a matrix unit such as 16: is unblocked by the closing of the tab switch 17a, a keying potential such as 8+ is applied to the diode gate 26 to render it conductive so that electrical tone signals pass to the voicing circuits 13. The construction and operation of the individual matrix units 16 is illustrated in FIG. 3.

FIG. 3 shows the key switch lla connected through its sustain keyer circuit 23a to the inputs of a number of the matrix units including the matrix unit 160. The output of the matrix unit 16c is connected as before described to the gate 26 between the audio signal source 12a and the voicing circuit 13a. The sustain circuit 23a is described below, but for the purpose of the present explanation, it can be said that the key switch lla is connected directly to the input of the matrix unit 160. Each matrix unit such as 160 includes an input resistor 27 and a control resistor 28 which are connected together at a common point, such point being connected to a diode 29 oriented to enable a keying potential to open the gate 26. In this embodiment, the size of the input resistor 27 has been made equal to the size of the control resistor 28, and the magnitude of the B+ potential as been made equal to the magnitude of the 8- potential with respect to ground. If the relative magnitude of the B+ and the B- potentials were made to be unequal, corresponding compensation in relative size of the resistors 27 and 28 would also be made. When the tab switch 17a is open, the source of B- potential is connected through a low impedance resistor 30 which biases the diode 29 to be nonconductive. If the key switch 11a were then closed, the combined potential of 8+ and B- would appear across the series connected resistors 27, 28 and the point between them would be at the same potential as ground. Thus, no gating potential could pass through the diode 29. When the tab switch 17a is closed to ground, then ground potential appears on a bus 31 which is common to all the control resistors 28 that are to be used for a given voice. When the key switch Ila is now closed, the B+ potential alone appears across the series connected resistors 27, 28 and the common point between them thus takes on a potential which is be that of the B+ potential, which readily renders the diode 29 conductive and also renders the gate 26 conductive to enable tone signals to pass from the audio signal source 12a to the voicing circuit that corresponds with the name given the tab switch 17a.

In some instances, if there is no interaction, it is possible to omit the diode 29 so that the input resistor is directly instead of indirectly connected to the control terminal of the electronic gate 26. The control resistor 28 and the resistor 30 are thus connected in series with each other and constitute biasing resistors, the biasing resistor 30 being in series with each of the various biasing resistors 28 that are associated with the various matrix units connected to the bus 31.

Ground potential is sometimes referred to herein as a third source of DC-potential which is of a level intermediate that of the source of B+ and the source of B- potentials.

The various audio signal sources 12 are so constructed that one extreme peak value of such signal has a potential which corresponds to such third source of DC-potential. The gate 26 includes a diode 26a, a diode 26b with corresponding terminals connected to a common point 26c therebetween which is the control gate. (By reversing all polarities, the same effect is achieved.) The signal source 12a is in effect a voltage reference or chopper which permits direct current to pass through the diode 26a to ground in pulses, thus causing corresponding voltage variations to appear at the anode of the diode 26b, which diode is optional but preferable. If the diode 29 be omitted, the biasing B- voltage with the tab switch 17a in an open position appears directly on the control terminal of the gate 26 and forcefully biases the diode 26a to nonconduction. With either of the diode-type of electronic gates 26b, 29 omitted, or with both present, the common point between the input resistor 27 and the-biasing resistor 28 is connected to control an electronic gate to control the circuit for transmitting keying potential to the voicing circuit 13a.

In FIG. 3, there is illustrated one of the sustain keying circuits or sustain keyers 23a. A Darlington transistor 32 has its collector connected to a source of B+ potential, an emitter connected to an output terminal 33 which is common to the inputs for the various matrix units 16a-c, and a base connected to be normally biased to render the unit nonconductive. A biasing resistor 34 connects the point 33 to a source of 8- potential which thus is connected to the emitter. A capacitor 35 is connected to the base and is normally charged with whatever bias is on the base. To that end, a source of B- potential is connected through the sustain tab switch 24 to a bus 36 which is common to all of the sustain keyers. The bus 36 is connected to the cathode of a diode 37, the anode of which is connected through a biasing resistor 28a to the base of the Darlington transistor 32. Thus, a 8- potential appears normally on the base as a bias and also correspondingly charges the capacitor 35. The base is further connected through a very high impedance 38 which is connected to B- at all times. The keying switch 11a is connected through an impedance 39 to the base of the Darlington transistor and to the capacitor 35. A fixed voltage reference comprising a Zener diode 40 is connected between ground and another terminal in the sustain tab switch 24.

With the voice tab switch 170 closed, the negative bias on the base of the Darlington transistor 32 renders it nonconductive. When the key switch 11a is closed, B+ potential passes through the impedance 39 which is very low, rapidly reversely charges the capacitor 35 and applies a positive bias on the base of the Darlington transistor which is of the NPN-type, thereby rendering it conductive so that a keying potential passes from the source, through the collector and to the point 33, whereupon keying occurs as previously described. When the key switch 11a is released, the 8- potential is conducted by the diode 37 and the resistor 28a to immediately reverse the charge on the capacitor and bias the Darlington transistor 32 to a nonconducting state. The impedance of the resistor 38 is so high that it has little effect on this part of the operation.

When the sustain keyer circuit 23a is to be used for sustain purposes, the tab switch 24 is moved to its other position so as to connect the sustain bus 36 to the voltage reference 40. The resistor 38 maintains the bias on the base of the transistor and when the key switch 11a is closed, the circuit operates as described previously. However, when the key switch 11a is released or opened, the capacitor 35 can discharge through discharge circuit means for effecting delayed discharge of said capacitance means for maintaining a progressively decreasing bias potential on the base of the transistor 32, and for thereafter providing the normal bias on such base. The lowest impedance path that the capacitor 35 has to discharge through is through the resistor 28a, the diode 37, and the voltage reference 40. The reference voltage typically has a reference value of +79% volts, so that the transistor bias provided by the capacitor 35 drops fairly rapidly to that voltage at which time conduction terminates. There is also a discharge path in the nature of base current through the transistor 32, and there is a discharge path through the high impedance resistor 38. Thus, a progressively decreasing keying potential will appear at the point 33 until the potential of the charge reaches the threshold value for the Darlington transistor 32 at which time it becomes nonconductive. Thereafter, the discharge path continues to reversely charge the capacitor 35. At any time that the key switch 110 is reclosed before the sustain has terminated, .the capacitor 35 will be immediately positively charged as previously explained and a new decay will begin.

In this circuit, the base of the transistor has biasing and gating potentials applied thereto which vary between B- and B+ and back to 8-. With the use of a Darlington transistor at this point in the circuit, no oscillation will occur. Further, depending upon the number of tab switches 17 that have been closed, a variable amount of impedance will be provided by the various parallel input resistors 27, but the sustain keyer circuit 23 including its discharge path is in no way affected by the selection of various impedances through which it must act.

Although there is a rapid discharge of the capacitor 35 when the key switch 11a is released, the fixed voltage reference provided by the diode 40 is well above that needed to render the Darlington transistor 32 nonconductive so that more than one decay rate is thus provided. When the sustain tab switch 24 is in the off" or illustrated position, the B+ potential also serves as a fixed voltage reference, but it is much less than that needed for rendering the Darlington transistor 32 nonconductive.

A modified or more sophisticated form of sustain keying circuit appears in FIG. 4a where corresponding numerals have been applied to like parts. The circuit collectively is referred to as sustain keyer 23b. As before, the Darlington transistor 32 has its collector connected to the source of B+ potential and its emitter connected through the resistor 34 to the source of B- potential, the emitter being connected to the input terminal 33 common to a number of matrix units as previously explained. The base of the transistor is connected through the resistor 28a through the diode 37 to the sustain bus 36 and thence to the tab switch 24 to the voltage reference 40 as previously explained. The high impedance resistor 38 is also connected between the 8- potential and the base. Here the capacitor 35 is connected a little differently, and in particular is connected between the base and collector of a PNP- transistor 41 which is normally biased to be nonconductive by a biasing resistor 42 which connects the base to a source of 8+ potential. The collector of the transistor 41 is connected to the base of the transistor 32, and the base of the transistor 41 is connected through an impedance means 43a, 43b to a key switch Md. The emitter of the transistor 4] is connected to a pulse line bus 44 and a 8+ potential is connected to the bus 44 through a resistor 45. With a B+ potential applied to both the emitter and the base of the transistor 41, it is normally biased to be nonconductive. The base is thus connected to the input terminal associated with the key switch 11d while the collector is connected to the base of the Darlington transistor 32.

One of the control tabs 25 mentioned above is an attack control switch 25b by which a B potential may be applied to all of the key switches 11 as a keying potential, and when the switch 25b is open, a different keying potential is applied. By way of example, where B+ is 19 volts and B- is 20 volts, those potentials are applied to a pair of series-connected resistors 46, 47 which are so sized that a positive keying potential of about l0 volts is provided thereon.

With the tab switch 24b closed and the tab switch 240 set or closed against the 8- potential contact, the sustain circuit 23b is off as previously explained for the circuit 230. Under this condition, the capacitor 35 is in series between the B+ potential and the 8- potential through the resistors 38 and 42.

When the key switch lld is closed, the base of the transistor 41 is made more negative and thus B+ potential will pass from the bus 44 through the transistor 41 to charge the capacitor 35. Upon release of the key switch the capacitor 35 will be rapidly discharged through the tab switch 240. When the tab switches 24a and 24b are connected in series to the voltage reference 40, the discharge will be more gradual. In this form of the circuit, with the capacitor 35 charged, the capacitor tends to keep the base of the transistor 41 more negative than the emitter where by current flows to the base of the transistor 32 to maintain its conductive bias. As the charge on the capacitor 35 dissipates through the discharge paths previously discussed, the base of the transistor 41 gradually becomes more positive until it is biased to nonconduction.

The components utilized in the sustain circuits are inexpensive and small. Normally, the capacitors used in sustain circuits are relatively large and expensive, but in the two forms of circuit here explained, very small inexpensive capacitors can be utilized so that a substantial saving per key is effected by use of this circuit.

The sustain tab switch 24 includes the section 24b which completely eliminates any discharge path through the bus 36 for the capacitor to either B- potential or through the voltage reference 40, thereby limiting the discharge path to one through the resistor 38. Under a switch setting where no discharge path exists through the tab switch 24, a very long sustain period is attained as the only path for current to flow is as base current and through the resistor 38.

l have found it advisable to provide a further transistor 48 of the NPN type with its collector connected to the sustain bus 36, its base connected through a capacitor 49 and a resistor 50 to 8+ potential and through a resistor 51 to B potential for squelching various unwanted couplings that occur when power is first applied to the instrument. Once the power supply comes on, the sustain squelcher performs no function.

in greater detail, this feature operates as follows. When power is first turned on the instrument both B+ and B- begin at volts and both gradually increase in magnitude. Thus, the potential between the collector and the emitter of the Darlington transistor 32 increases. At the same time, the B+ potential applied to the resistor 42 and hence the base of the transistor 41 as well as the B-lpotential on the emitter thereof gradually increase enabling a 8+ potential to build up fairly rapidly across the capacitor 35, and hence on the base of the Darlington. The B- potential that should be biasing the base of the Darlington transistor 32 must build up through the high impedance 38 and this takes longer, and therefore a situation has occurred wherein all of the tone signal sources are simultaneously initially keyed. This is the condition that the squelcher transistor 48 corrects. In that its emitter and its base are both connected to B- potential that increases from zero and in that its collector is connected to the base of the Darlington transistor 32 through the diode 37, the transistor 48 is normally nonconductive and thus has no effect, except at startup. The capacitor 49 is relatively large, and during the time that 8+ is building up from 0, there is a progressively increasing charge across the capacitor 49 which turns on the transistor 48, whereby any positive potential on the base of the Darlington transistor 32 is quickly dissipated through the resistor 28a, the diode 37 and through the collector and emitter of the transistor 48. The Darlington transistor 32 has a threshold voltage of about l .2 volts that needs to be applied to the base to make it conduct, while the diode has a threshold potential of about 0.6 volts, and therefore, any transient positive charge that might begin to build up on the base of the Darlington transistor 32 is quickly and more readily dissipated through the sustain squelcher circuit. The capacitor 49 serves no function except during the initial buildup of the B+ potential to supply a gating potential for the period of time needed for the Darlington transistor 32 to become negatively biased through the resistor 38. I

Thus, in FIG. 4a at 23b, between the pulse bus 44 and the sustain bus 36, there is connected only one sustain keyer circuit 23b under the control of one key switch lid, in an actual instrument, such circuit being repeated for each of the other 43 key switches ll. The sustain squelcher thus is common to all of the sustain keyers 23 as are the sections of the tab switch 24. When the key switch 1 Id is closed, a keying potential thus appears at the emitter of the Darlington transistor 32 which is directly connected to the common input terminal 33 of the various matrix units 160 etc. Thus, all of the structure of FIG. 3 that is connected between the buses 31 and 36 is repeated for that number of times as is necessary to provide each of the key switches 11 with one of the sustain circuits 23a or 23b and the set of matrix units connected to the terminal 33. This is the structure utilized for producing conventional organ tones of selected attack and of selected sustain.

The remainder of the circuitry on F IGS. 4a and 4b includes a plurality of presets, one of which is shown at 18, the circuitry for providing the percussion l9 and repeat 22, the detector 21 and the percussion and repeat tab switches 20. From FIG. 1, it is noted that the detector senses normal playing of the organ and that the other components mentioned all act on or are connected to the matrix 16. ln FIG. 3, at the tab switch 17a, there is shown a terminal 52 which in a schematic way denotes a point where the remainder of the circuitry of FlGS. 4a and 4b connects into the circuitry of FIG. 3.

In order to have percussion signals, it is necessary that the keying envelope be precisely synchronized with the closing of a key switch 11. To that end, the pulse bus 44 is provided to which all of the sustain keyers are connected. Each time that the transistor 41 is rendered conductive, there is a drop in potential across the resistor 45, and that voltage drop is sensed by a pulse sensing transistor 53 of the PNPtype. The emitter and base of the transistor 53 are respectively connected to 8+ potential through a pair of resistors 54, 55 so that the transistor is biased to nonconduction. The collector of the transistor 53 is grounded through a resistor 56. A capacitor 57 is connected between the base and the collector of the transistor 53. The resistor 55 and a variable resistor 58 are connected in series between B+ potential and ground, and the junction between them is connected to the base of the transistor 53 and through a resistor 59 and capacitor 60 to the pulse bus 44. The capacitor 60 thus has both of its terminals connected to 13+ potential and when the transistor 41 goes conductive, the capacitor 60 immediately becomes less positive to provide a momentary less positive condition of the base of the transistor 53 whereby 8+ is conducted through the emitter and the collector and the resistor 56 to provide a posi tive pulse of short duration. The positive pulse is lengthened a bit by the presence of the capacitor 57. The variable resistor 58 is used to lower the biasing potential on the base of the transistor 53 by a very slight amount, and in no instance by an amount so great that the base would be negative and hence the transistor conductive. lts effect thus is to lessen the amount of additional negative going pulse or threshold needed to sense such pulse. The positive going pulse is coupled by a capacitor 61 to the base of a pulse amplifying transistor 62 of the NPN- type. The base thereof is also connected to the common point of a voltage divider formed by a resistor 63 and a variable resistor 64 that are connected in series between B+ potential and ground. Again, the resistor 64 is adjusted to determine the sensitivity or threshold value of the transistor 62 as its collector is connected through a resistor 65 to B+ potential. The collector of the transistor 62 is connected to a grounded capacitor 66 and a capacitor 67 for coupling the signal to an isolation diode 70, the tenninals of which are connected by a pair of resistors 68, 69 to B+ potential. The diode 70 is oriented with the cathode connected to the capacitor 67. When the transistor 53 has sensed the depression of a key switch and has created a weak negative-going'pulse, that pulse is in effect amplified by the transistor 62 by virtue of the sudden discharge of the capacitor 66 through the transistor 62 so that a strong negative-going pulse is coupled by the capacitor 67 to the diode 70 to render it conductive.

The negative-going pulse is coupled by a resistor 71 to the base of a PNP-transistor 72 whose emitter is connected through a resistor 73 to a 8+ potential, whose base is connected by a capacitor 74 to its collector and whose collector is connected by a resistor 75 to ground. The transistor 72 serves as an amplifier and because of the capacitor 74, also increases the duration of the pulse. Further, the pulse that it delivers is a positive-going pulse. The transistor 72 is biased to be nonconductive as B+ potential is applied to the emitter and as B+ potential is also applied through the resistors 69, 71 to the base. The negative-going pulse thus charges the capacitor 74 and renders the transistor 72 conductive. The output pulse is obtained from the collector and is coupled by a capacitor 76 through a resistor 77 to a transistor 78 of the NPN-type. The transistor 78 has a collector that is connected through a resistor 79 to a source of potential which is about that of ground. In this embodiment, I use instead of ground a potential of +3 volts for the purpose of having sufficient potential to overcome the thresholds of various diodes where a potential of substantially ground value is employed. The emitter of the transistor 78 is connected to B- potential, while the base is biased by the resistor 77 and a resistor 80 to 8- potential, for biasing the transistor 78 to be nonconductive.

When the positive pulse is sensed at the collector of the transistor 72, it thus also charges the capacitor 76, which is relatively large, to provide a gating potential at the base of the transistor 78 to render it conductive, the capacitor 76 gradually discharging after the capacitor 74 has discharged. When the transistor 78 is conductive, it overrides signals coming from the repeat circuit 22 described below the initiates signals in lieu thereof.

The repeat 22 constitutes a source of pulse signals having a plurality of phases, and in the disclosed embodiment, a conventional multivibrator is used that has two phases. A pair of Darlington transistors 81, 81 each have a collector that is connected to the +3 volt source through a resistor 82, 82. Each collector is also connected through a capacitor 83, 83 to the base of the other transistor 81, 81. The emitter of each transistor 81, 81 is connected to B- potential, one through a diode 84 and the other through a double diode 85. As the diodes 85 have twice the threshold of he diode 84, the circuit is rendered asymmetrical so that oscillation will always begin. Each base is also connected through a resistor 86, 86 through a common resistor 87 to the +3 volt potential, the common point of the resistors 86, 86 being connected through a resistor 88 to the wiper of a potentiometer 89 whose ends are connected to the 8+ and B- potentials. THe potentiometer 89 serves as a speed control for determining The rate at which the pulse generator or repeat multivibrator 22 will oscillate.

The transistors 81, 81 are of the NPN-type. Each of the collectors constitutes an output terminal 90, 90 that is connected to the anode of a diode91, 91 which are connected together to one of the control tab switches 25a, through which a B- potential is obtained forbiasing the repeat circuit or multivibrator 22 in an off position. When the switch 250 is actuated, such bias is removed. As the internal construction and operation of the multivibrator circuit per se is conventional, it is believed that no further description of its operation is necessary. It is sufficient to state that at one of the output terminals 90, there appears a square wave and at the other of the output terminals 90, there also appears a square wave, the waves being out of phase with each other, and where there are two phases, the extent is l80 out of phase with each other.

Each of the output terminals 90 is connected to a capacitor 92, 92, the other side of which capacitors are connected to the +3 volt potential through a resistor 93, 93. The capacitors 92, 92 are more thancoupling capacitors in that their charging time is much less than the duration of one square wave pulse from the multivibrator. Thus, during the charging time, a short duration pulse is created that passes through a diode 94, 94 to a line 95 for one phase and to a line 96 for the other phase.

Each of the lines 95, 96 is connected through a resistor 97 to the base of a transistor 98, 98 of the PNP-type whose emitters are connected to +3 volt potential, and whose bases are connected through a resistor 99, 99 to the same potential to bias the transistors 98 in an "off" condition. A capacitor 100 connects each of the collectors to the bases and the output of the transistors 98 is taken from the collectors. The collectors are each connected to a pair of diodes 101, 102. The diodes 101 are each connected through a resistor 103, 103 through a common resistor 104 connected to a further common resistor 105 and thence to 13- potential. The diodes 102, 102 are connected by resistors 106, 106 to the point between the common resistors 104, 105. Thus, a B- potential is available at the collectors of the transistors 98. The capacitors 100 thus have a charging path from the source of +3 volts, through the resistor 99, in parallel through both of the diodes 102, the resistor 104 and the resistor 105. Because of the polarity of the diode 94, the pulse from the pulse generator on each of the lines 95, 96 is negative-going and is coupled by the resistor 97 to the bases of the transistors 98 to make them instantly less positive than their emitters whereby they are immediately rendered conductive, thus instantaneously discharging the capacitors 100 and making the collectors sharply more positive than they had previously been. As the capacitors are connected between the base and the collector, the charge is restored, thereby progressively making the transistors 98 less conductive and hence a sawtooth waveform is generated, once for each cycle of the repeat circuit 22, there being one such pulse in each phase which are out of phase with each other. The transistor 98, 98 thus serve as control pulse shapers. Since these can be called upon to drive many circuits, it is preferable to provide a current amplifier generally indicated at 107 for each pulse line 95, 96. Each current amplifier 107 includes a Darlington transistor 108 of NPN-type and a further transistor 109 of the same type. Each transistor has its collector connected to +3 volts through a resistor 110 and 111 respectively and its emitter connected to B- potential through a resistor 112 and 113 respectively. The collector of the shaper transistor 98 is connected to the base of the transistor 108, which is biased to be off, and the emitter of the transistor 108 is connected to the base of the transistor 109 which is also biased to be off. When the sawtoothed control signal which is positive-going is applied to the base of the transistor 108, it becomes conductive and its collector potential renders the transistor 109 conductive to provide an amplified signal on a bus 1 14 associated with the first phase and a bus 115 associated with the other phase. The current amplifier 107 serves to drive the circuits connected to the percussion bus 114, while the other current amplifier 107 serves to drive the circuits associated with the percussion bus 115. Each of the percussion buses has eight switching circuits thereto. Each of those switching circuits which are 16 in number includes a resistor 116 connected to the anode of a diode 117 which is connected to the base of a Darlington transistor 118. The transistors 118 have their collectors grounded through a resistor 119, their bases biased through a resistor 120 to 13- potential and their emitters biased through the resistor 30 to B- potential and their emitters biased through the resistor 30 to B- potential whereby they are normally nonconductive. When one of the positivegoing sawtooth control pulses is received from the bus 114 or 115, the Darlington transistor 118 becomes conductive in accordance with the shape of that pulse and its emitter terminal 52 goes sharply to ground potential and thereafter decreases to B.

The resistor 30 and the terminal 52 also appear on FIG. 3 wherein the terminal 52 is common to many of the repetitions of FIG. 3 as explained below and wherein the terminal 52a is a duplicate of the terminal or bus 52 but separate therefrom. As the terminal 52 is common to numerous control resistors 28, the respective audio signal sources 12 associated therewith will thus be given or subjected to a keying signal that is further modified by the shape of or the envelope of the generally sawtoothed pulse.

When the percussion repeat or control tab switch 250 (FIG. 4a) is turned on" to activate the pulse generator or multivibrator 22, B- potential is also applied directly to all of the key switches 11, thus overriding any selection of slow attack, where fast attack is needed for percussion. Another section of the same switch 25a is arranged to apply either B- or +3 volts through a line 121 to one side of each of the percussion and repeat tab switches 20 (FIG. 4b). In this embodiment, the percussion envelope switching has been illustrated as being solely connected to one voice, for example flute voicing. However, that flute voicing in this embodiment has eight different ranks, each provided with a percussion control switch 20. Typically, they may be associated with the l-foot, the Ila-foot, the 2- foot, the 2%-foot, the 4-foot, the SA-foot, the 8-foot, the the 16-foot ranks. One such switch 20a is connected by a line 122 to the cathodes of two diodes 123, 123, the anodes of which are respectively connected into the phase channels between the resistor 116 and the diode 117. When the tab switch 250 (FIG. 4a) is in the off position, a B- potential is applied through the line 121 to the "on contacts of all the switches and the same potential is also applied to all the off" contacts of the same switches. Thus, any of the tab switches 20 can be selected in advance and each stays depressed until reactuated. Thus, even though any combination of those switches might be actuated, only a B- signal will pass out through the line 122 and through the diodes 123 to provide a negative bias which cancels any sawtooth signals. When the tab switch 250 is moved to the on" position, then a potential of +3 volts is brought to the on" contacts, which is in effect ground, and to the common point between the diodes 123. Thus, a reference is provided for each of the phase channels thatenables the sawtooth signals to pass through the circuitry as previously explained.

In FIG. 3, the relationship between the tab switch and the bus 52 is somewhat simplified. In FIG. 4b, the tab switch 17a has a stationary contact secured to the positive 3-volt source of potential, which is analogous to ground, and the movable contact thereof has a path by which it reaches the point 52. To this end, the switch 170 is connected by a line 124 through a resistor 125 to the collector of an NPN- transistor 126 whose emitter is connected to'B-. The base of the transistor 126 is connected through a resistor 127 to the pointbetween the diodes 123, 123. The collector of the transistor 126 is connected to the anodes of a pair of diodes 127, 127 whose cathodes are connected to the phase channels between the diodes l 17 and the transistors 118.

As the transistors 118 are normally biased to be nonconductive by virtue of the potential applied through the resistor 120, in order for them to conduct, a gating potential is applied. One of the tab switches 17a associated with a percussive voice can apply a positive 3-volt potential through the line 124, the resistor 125 and each of the diodes 127 to overcome the bias of the resistor 120 and to provide a base bias which is approximately the same as that on the collector. The tab switch 17a thus enables production of that particular tone with a full signal.

Several of the present circuits 18 may be provided in a particular instrument and one is shown here for illustration. A

sistor 128 so that a slightly lesser potential is applied to the line 124. The resistances 128-135 are selectively sized to provide the desired proportion of volume from each of the ranks.

1f the tab switch 170 is closed or if the preset switch 18a is closed to provide the 3 volts of potential as described, such potential is also applied to the collector of the transistor 126 which is normally nonconducting. When one of the percussion envelope switching tab switches 20 is selected by being closed to the line 121 and the tab switch 250 is in the on" position, the 3-volt positive potential also appears at the base of the transistor 126 to render it conductive whereby the control signal from the tab switch 17 or the preset 18 is dissipated to the B- potential source. Thus, the tab switch selection and the preset selection is overridden by the percussion switch 20 whereby the same rank is involved, but not otherwise. The diodes 117 isolate a particular selected circuit from others connected to the same bus 114 or 115.

The following is a summary, then, of the switching action that can take place. With the percussion switches 20 off, a B- potential conducted by the diodes 123 blocks any percussion envelope signal between the resistors 116 and the diode 117 associated with one tab switch 20, and such signal is isolated by the diodes 117 from having any effect on the transistors 118. With the tab switches 17 open and the preset switches 18 open, that are associated with a particular switching circuit associated with one tab switch 20, the transistors 118, 118 are biased to be nonconductive. 1f the tab switch 200 is depressed so as to be on, a potential of +3 volts is brought by the line 122 into the circuit which has no particular effect under that condition except that it clearly 'constitutes an absence of any blocking bias for the phase channels whereby the sawtooth-type signals can appear on the bases of the Darlington transistors 118 and overcome their normal bias to render such transistors conductive in accordance with such envelope. Further, with the percussion switch 20a set to block both phase channels as just described, either or both of the tab switch 17a or the preset 18a can bring in a biasing potential through the diodes 127 to turn on the respective Darlington transistors 118 so that the point 52 is grounded (thereby corresponding to closing the switch 17a to ground in H0. 3). Under this condition, normal nonpercussion playing of the organ takes place. With a preset 18a or tab switch 17a in the on" position, and with the percussion tab switch 20a in the on position, the transistor 126 is rendered conductive, the potential in the line 124 is dissipated to the B- potential, and thus the tab switch 17a and thepreset 18a are overridden by the repeat tab switch 20. The use of the two diodes 123 and the two diodes 127 in this switching circuit isolates the one phase channel from the other phase channel.

As explained above, each percussion channel delivers its own train of sawtoothed pulses where one train is out of phase with the other. Means are provided to alter the duration or length of the sawteeth, and in the present embodiment, that length has a range of adjustment from about 20 milliseconds to 2 seconds. For this purpose, there is provided a potentiometer 137 (FIG. 4b) which serves as a voltage divider between 8- potential and ground for obtaining a potential that is referenced with respect to ground potential by a resistor 138. The selected potential is coupled by a resistor 139 to the base of an emitter-follower transistor 140, the base being further biased by a resistor 141 connected to B- potential. The transistor 140 is of the NPN-type and its collector is connected through a resistor 142 to the source of 3-volts positive potential, and the emitter is connected through a resistor 143 to 8- potential. The emitter is further connected to one side of a capacitor 144, the other side of which is connected to B- potential. The emitter is further connected to the common point between the resistors 103 and to one end of the resistor 104. Normally, there is some B- potential picked up from the potentiometer 137 which is in parallel with the B potential obtained from the resistor 141 to bias the base of the transistor 140 so that it is less negative than its emitter, whereby the transistor 140 is partially conductive. The resistor 142 is very small and so the emitter of the transistor 140 has a potential that is governed by the setting of the potentiometer 137, and which thus provides a voltage reference at the common point of the resistors 103, 103, and 104. The circuitry thus described in combination with the resistors and diodes connected thereto that lie intermediate the transistors 98, 108 serve to provide various paths for recharging the capacitor 100. It is stated above that a negative-going pulse received on the line rendered the transistor 98 conductive to discharge the capacitor 100 rapidly to produce the vertical portion of the positive-going sawtooth waveform. The various resistors and diodes thus provide alternate paths for recharging the capacitor 100. The lowest impedance path from the B- potential includes the resistor 105, the resistor 106 and the diode 102. 1n parallel with the resistor 106 and the diode 102 there is the resistor 104, the resistor 103 and the diode 101. A further parallel path is provided from the resistor 112 in the form of base current. At the outset of charging, the impedance is lowest, and thus the ramp side of the sawtooth waveform has its steepest slope at the outset or top as all of the charging paths are in parallel. When the voltage drop across one of the diodes 101, 102 decreases below its lowest threshold, that branch falls out of the circuit and the remaining branches or pairs of charging paths jointly provide a second slope which is not as steep. When the voltage drop across the other diode falls below its threshold value, it also causes that branch or charging path to become ineffective. Lastly, when the base potential of the Darlington transistor 108 falls below its threshold value, the ramp of the sawtooth waveform has been complete.

Another of the control tab switches is identified in FIG. 4a as 250 which has one section that like the tab switch 25a provides 8- potential to the key switches 11, such as those that are associated with the upper manual of an organ. The effect of using this switch is to override the setting of the attack switch 25b without turning the pulse generator or multivibrator 22 on". Another section of the switch 250 just like the corresponding section of the switch 25a, applies a positive 3 volts to the line 121 as previously explained. With percussion on" and with repeat off, and with the selection of the appropriate one or more of the percussion switches 20, when a key switch 11d is depressed, a potential passes from the Darlington transistor 32 of the sustain circuit and thence to terminal 33 on FIG. 3 as previously explained. In addition, such keying was sensed by the pulse sensor, collectively referred to herein as the detector 21, and specifically including the circuitry associated with the transistors 53, 62, 72 and 78. It is stated above that the transistor 78, which is a percussion trigger device, is normally nonconducting and has the 3- volt positive potential applied through the resistor 79, thence through the collector and emitter of the transistor 78 to the 8- potential. Thus, when the transistor 78 is made momentarily conductive, a strong negative pulse appears on the cathodes of two diodes 145, 146 and also on two diodes 147,

148. The diodes 145-148 are thus connected to the collector of the transistor 78. The negative pulse thus obtained by the conduction of the transistor 78 appears simultaneously on both of the phase lines 95, 96 so that during the initial instant of the playing of a key, all the selected circuitry associated with both of these lines is initially simultaneously actuated. With the repeat 22 turned ofi, one such pulse will thus pass down the phase channels as previously described but with everything taking place in each channel in phase.

When the percussion repeat switch 25a is actuated to remove the inhibiting bias from the repeat circuit 22, then the pulse generator oscillates continuously, sending a negative pulse first down one of the phase lines 95, 96 and then down the other. With the repeat circuit 22 oscillating when the key' switch lld is closed, the strong negative pulse that was sent down the lines 95, 96 is also conducted by the diodes 147 and 148 to appear momentarily at the terminals 90, 90 in the same manner as the inhibiting voltage to briefly override or stop the multivibrator for the duration of such pulse, and upon the termination of such pulse, the pulse generator 22 automatically begins sending out alternate pulses for alternately keying circuits associated with the two branches during the time that the key switch 11d is held depressed or that a note is sustained by the sustain circuit portion.

With reference to FIG. 4b, the circuitry illustrated as being connected to the buses 114 and 115, the tab switch 20a, and one of the sections of the preset 18a is duplicated for each of the other percussion tab switches 20 so that each is connected in the same manner to the buses 114, 115 and to one of the lines corresponding to the line 122. Any number of the percussion tab switches 20 may be selected for use and each serves to override corresponding tab switch selections or preset selections.

The 2-phase channels respectively terminate in the terminal such as 52, 52a etc., one for each phase. The terminal 52 is a bus that is connected to control the keying circuits described which are associated with half of the tone signal sources of one ranksuchas E, F, F#, A#, B and C. The bus 52a is connected to control the tone signal sources for the same rank representing the notes G, G#, A, C#, D and D#. Where repeat is used, a

it is unlikely that two notes such as E and F will be simultanetaneously played. The use of the two channels herein described would thus initially, under the control of a percussion switch, produce both frequencies after which E and G would alternate, for instance, in the style that a marimba is played. Thus, there are at least two buses such as 52, 52a for each selected voice.

In FIGS. 1-4, the principles of construction have been illustrated with repetition of illustration being omitted wherever practical. However, when all of the circuits are duplicated or repeated as herein described, there are certain relationships that exist that are not clearly evident from the drawings thus far described. Accordingly, FIG. 5 illustrates in a convenient form a portion of the switching circuitry that is thereby provided. In particular, this involves the use of more than one of the series of matrix units 16a etc. shown in FIG. 3.

As shown in FIG. 5, representative connections have been provided to assist the reader in visualizing the connection between the various phase channels, the various matrix units, and the various key-operated sustain circuits. At the top of FIG. 5, the key switch 11e, like the key switch 11a, is connected to the sustain keying circuit 23b shown on FIG. 4b, and a further key switch 11f is connected to another identical sustain keying circuit 230. Both of these sustain circuits are connected to the buss 44 so that the detector 21 can sense key switch closing as previously described. The output of the Darlington transistors 32, 32. is shown connected directly to the common point or terminals 33, 330 that constitute the inputs to the various matrix units. The first matrix unit for each key is connected to control the sound signal sources 12e, 12f respectively, both such matrix units being subject through their control resistors 28 to be subject to the further control of one of the 16 Darlington transistors 118. Such control would apply to half of the instrument as explained above, and the bus 31 would be common to other matrix units, but ordinarily not more than one from a particular key switch. Thus, the second matrix unit associated with the key switch He is arranged to control the signal source 12f and is under the control of a different one of the Darlington transistors 118, for instance, an octavely related one. The output of the matrix unit would then go to a different bus 31a. The second matrix unit associated with the key switch 11f is under the control of such second Darlington transistor 118 just mentioned. Although the two Darlington transistors 118, 118 shown in FIG. 5 are associated with different footages of the same note, a rather similar arrangement is present where they are separated as shown in FIG. 4b.

The following values are representative:

Resistors Capacitors Voltages 17-K 35-005 mfd. 11+

19V pus. Ill-K 49-10 mfd. B-

ZUV ncg. ZHu-ISOK 57-002 mld. JO-IK 6041.47 rnfd. 34-1UK (ll-0.22 ml. 38-( FIG. 3) 22 meg 6641.02 mfd.

(FIGS. 40 and 5) 3.3 mcg 67-022 mi'd. 39-39K 74-002 mfd. 42-1 meg 76-].0 ml'd. 4311-47K 83-10 mfd. 43h-22 K 920.l mfd. 45-10 ohms 100-0047 mfd. 46-470 ohms 144-35 mfd. 47-2.7K

SCI-47K RESISTORS 54-100 ohms 1042.2K 143-2.2K 55-4.7K 2.7K 149-10 ohms 56-10K 106-22K 150-82K SID-25K -10 ohms 151-4.7K 59-4.7K 111-10 ohms 63-470 ohms l12-22K 64-5OK 113-4.7K 65-10K l16-2.2K 68-1OK 119-l0 ohms 69-10K l20-22K 71-4.7K l25-2.2K 73-10 ohms 127-IOK 75-4.!K 128-IK 77$.6K 129-2.2K 79-4.7K -63 K ao-4.7| [Al-4.7K 82-4.7K 132-4.?K 86-27K [SS-4.7K 87-1OK l34-l5K 88-2.2K 11 -4.7K 89-1014 137-1QK 93-1OOK 138-2.2K 97-56K l39-22K 99-22 meg Lil-4.7K 103-Z2K 142-10 ohms Although various minor modifications might be suggested by those versed in the an, it should be understood that I wish to embody within the scope of the patent warranted hereon. all such embodiments as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. An electronic musical instrument, comprising:

a. a key-operated switch for being connected to a first source of DC-potential;

b. an electronic gate having a control terminal;

c. an input resistor connecting said key-operated switch to said control terminal;

cl. a first and a second biasing resistor connected in series with each other and for being connected between a second source of DC-potential and the end of said input 5 resistor more remote .from said key-operated switch;

e. a tab switch for being connected between a third source of DC-potential and a point between said first and second biasing resistors, said third source of DC-potential being of a level intermediate that of said first and second sources of DC-potential;

f. a source of AC-potential of audio frequency having one extreme peak value corresponding to said third source of DC-potential; and

g. means for converting electrical audio signals into sound and connected by said electronic gate to said source of AC-potential;

h. said electronic gate being oriented to conduct current when a potential having a polarity opposite to that of said one extreme peak value is applied thereto.

2. An electronic musical instrument according to claim 1,

including:

a. a pulse generator connected to be activated in response to closing of said key-operated switch; and

b. means including a second tab switch for connecting said pulse generator to said point between said first and second resistors.

3. An electronic musical instrument according to claim 2 including:

a. a further input resistor, a further first and second biasing resistor, a further source of AC-potential and a further electronic gate, all connected to said key-operated key switch as set forth in claim I;

b. means including a third tab switch for connecting said pulse generator to said point between said further first and second resistors; and

c. a percussive control tab switch connected to control the effectiveness of said second and third tab switches.

4. An electronic musical instrument according to claim 1 including presetting means connected in electrical parallel with said tab switch for selectively providing a lesser potential to said point.

5. An electronic musical instrument according to claim 4, including: I

a. a further input resistor, a further first and second biasing resistor, a further tab switch, a further source of AC- potential, a further electronic gate, and a further presetting means, all as set forth in claims 1 and 4; and

a switch connecting both of said presetting means to said third source of potential.

6. An electronic musical instrument according to claim 1, including: a further key-operated switch, a further input resistor, a further first and second biasing resistor, and a further tab switch, all connected as set forth in claim 1, whereby when said source of ACpotential is simultaneously gated by parallel paths, each including one of said key-operated switches and one of said input resistors, the amplitude of potential reaching said converting means will be increased.

7. An electronic musical instrument according to claim 1, including:

a. a pulse generator connected to be activated in response to closing of said key-operated switch, said generator being of the type operative to provide a train of pulses; and

b. means including a second tab switch for connecting said pulse generator to said point between said first and second resistors.

8. An electronic musical instrument according to claim 1,

including:

a. n--! further input resistors, n-l additional first and second biasing resistors, n-I further sources of AC-potential and n-1 further electronic gates, all connected as set forth in claim 1; V

b. a pulse generator connected to be activated in response to closing of said key-operated switch, said generator having n outputs where n is at least 2, said generator being of the type operative to provide a series of pulses to each output and the pulses of each series being spaced in time from the pulses of the other series; and I means including further tab switches for connecting the outputs of said pulse generator to said points between said n pairs of first and second resistors.

9. An electronic musical instrument according to claim 1, in which said tab switch is a presetting means having impedance means for providing a potential at said point which is less than that of said third source of DC-potential.

10. An electronic musical instrument comprising:

a. a series of sources of AC-potential signals of audio frequency;

b. a plurality of voicing circuits for shaping said audio signals;

I c. means connected to said voicing circuits for converting said audio signals to sound;

d. a matrix assembly for keying said sources and thereby coupling them to said voicing circuits;

e. a series of key switches connected to control said matrix assembly;

f. a series of tab switches connected to said matrix assembly for connecting certain of said sources to certain of said voicing circuits; and

g. a repeat circuit connected to said matrix assembly for periodically interrupting the connection from said key switches to said matrix assembly.

11. An electronic musical instrument according to claim 10 including switching means for controlling said repeat circuit and including a separate switch for each of certain of said tab switches.

12. An electronic musical instrument according to claim 11 in which there is one such separate switch for each of said tab switches associated with the various frequency ranges of one voice, the voicing circuits of other voices being unafiected by said repeat circuit.

13. An electronic musical instrument according to claim 10 including a series of sustain keying circuits respectively connected between each of said key switches and said matrix assembly for providing repetition of tone signals during the decay produced by said sustain circuits.

14. An electronic musical instrument according to claim 10 in which said repeat circuit includes a pulse generator having n phases providing a plurality of n trains of pulses, the pulses of each train being out-of-phase with each other train, and each train being connected to control the repetition of l/n of said sources.

15. An electronic musical instrument according to claim 14 including means responsive to the actuation of said key switches and connected to said pulse generator for simultaneously activating said n phases once after which said phases resume said out-of-phase operation.

16. An electronic musical instrument according to claim 14 including:

a. n means connected to the outputs of said pulse generator for respectively shaping the pulses of each train of pulses; and

b. a single means connected to each of said shaping means for simultaneously controlling the shaping means to determine the envelopes of their output wave forms.

27. An electronic musical instrument according to claim 10,

including a percussion circuit connectedto said matrix assembly and responsive to said key switches for controlling a selected portion of said matrix assembly to provide a control signal having a percussive envelope.

18. An electronic musical instrument according to claim 17, including switching means for controlling said repeat and percussion circuits and including a separate switch for each of certain of said tab switches.

19. An electronic musical instrument according to claim 10, in which said tab switches include a presetting means having impedance means for providing a reduced potential at said matrix assembly.

20. An electronic musical instrument comprising:

a. a series of sources of AC-potential signals of audio frequency;

b. a plurality of voicing circuits for shaping said audio signals; i

c. means connected to said voicing circuits for converting said audio signals to sound;

d. a matrix assembly for keying said sources and thereby coupling them to said voicing circuits;

e. a series of key switches connected to control said matrix assembly;

f. a series of tab switches connected to said matrix assembly for connecting certain of said sources to certain of said voicing circuits; and

g. a percussion circuit connected to said matrix assembly and responsive to said key switches for controlling a selected portion of said matrix assembly to provide a control signal having a percussive envelope.

2!. An electronic musical instrument according to claim 20 said percussion circuit having a single detector responsive to all of said key switches.

22. An electronic musical instrument according to claim 20, said percussion circuit having switching means for controlling said percussion circuit and including a separate switch for each of certain of said tab switches.

23. An electric musical instrument according to claim 22 in which there is one such separate switch for each of said tab switches associated with the various frequency ranges of one voice, the voicing circuitsof other voices being unaffected by said percussion circuit.

24. An electronic musical instrument according to claim 20 in which said percussion circuit includes a pulse generator having n phases providing a plurality of n trains of pulses, the pulses of each train being out-of-phase with each other train, and each train being connected to provide a percussive envelope for the control of a predetermined portion of said matrix.

25. An electronic musical instrument according to claim 24, including means responsive to the actuation of said key switches and connected to said pulse generator for simultaneously activating said It phases once after which said phases resume said out-of-phase operation.

26. An electronic musical instrument according to claim 24, including:

a. it means connected to the outputs of said pulse generator for respectively shaping the pulses of each train of pulses; and

b. a single means connected to each of said shaping means for simultaneously controlling the shaping means to determine the envelopes of their output wave forms.

27. An electronic musical instrument according to claim 20, in which said tab switches include a presetting means having impedance means for providing a reduced potential at said matrix assembly.

28. An electronic musical instrument according to claim 20, having switching means connected to and controlled by said percussion circuit and forming a part of the connection to said matrix assembly, said switching means enabling said percussion circuit to disable certain of the connections between said tab switches and said matrix assembly during operation of said percussion circuit.

29. An electrical musical instrument according to claim 28, having a series of presetting means connected in electrical parallel to said tab switches and disabled by said switching means along with said certain of the connections to the matrix assembly.

30. An electronic musical instrument according to claim 20 in which corresponding elements of said key switches are electrically common, means connected to said electrically common elements for selectably providing one of a plurality of potentials thereto for controlling the rate of attack of the keyed tone signals, and a switch forming a part of the connection between the percussion circuit and said matrix assembly and being further operative to apply a potential to said electrically common elements which effects a desired rate of attack.

31. An electronic musical instrument according to claim 20 in which said percussion circuit has a plurality of separate switches for each of a plurality of tab switches, and a further master tab switch for controlling said percussion circuit.

32. A sustain keying circuit for an electronic musical instrument comprising:

a. a Darlington transistor having a collector connected to a source of keying potential, a base connected to be normally biased to be nonconductive, an emitter connected to an output terminal;

b. capacitance means connected to said base and normally charged with the bias on said base;

c. an input terminal for receiving a keying potential and connected to said base and capacitance means for reversely charging said capacitance means and rendering said Darlington transistor conductive;

d. discharge circuit means connected to said capacitance means for effecting delayed discharge of said capacitance means in response to removal of said keying potential for maintaining a progressively decreasing bias potential on said base, and for thereafter providing the normal bias on said base; and

e. means connected to the base of said Darlington transistor and responsive to the initial buildup of potentials in said circuit for dissipating any bias potential that would render said Darlington transistor conductive before its normal bias is applied.

33. An electronic musical instrument, comprising:

a. a source of DC-keying potential;

b. a source of AC-potential of audio frequency;

c. means for converting an electrical audio signal into sound;

d. means connecting said source of AC-potential to said converting means and including a first electronic gate;

e. means connecting said source of DC-keying potential to said first electronic gate, and including a second electronic gate;

f. said second-named connecting means including a key switch connected to said source of DC-keying potential, and a sustain circuit directly connected to said key switch, responsive to the closing thereof, and forming part of the connection to said second electronic gate; and

g. a tab switch connected to control said second electronic gate.

34. An electronic musical instrument according to claim 33,

in which said sustain circuit includes:

a. a Darlington transistor having a collector connected to the source of keying potential, a base connected to be normally biased to be nonconductive, and an emitter connected to said second electronic gate;

b. capacitance means connected to said base and normally charged with the bias on said base;

c. an input means connected between said key switch and said base, for reversely charging said capacitance means for rendering said Darlington transistor conductive; and

d. discharge circuit means connected to said capacitance means for effecting delayed discharge of said capacitance means in response to opening of said key switch for maintaining a progressively decreasing'bias potential on said base, and for thereafter providing the normal bias on said Darlington transistor and said second electronic gate; and base. b. a biasing resistor connected between said tab switch and 35. An electronic musical instrument according to claim 34, said second electronic gate electronic gate. including: 1 :1: 1* 1 a. an input resistor connected between the emitter of said 5 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,627,895 Dated December 14, 1971 Inventor(s) Peter T. Savon It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover page, correct the title to read ELECTRON 1C MUSICAL INSTRUMENT WITH DIRECT CURRENT KEYING OF PLURAL MUSICAL EFFECTS- C01. 5, line 72 change to ---B m;

C01. 10-, lines 21 and 22 delete "and their emitters biased through the resistor 30 to B potential";

Col. 11, line 29 change "B+" to --B- Col. 12, line 63 change "complete" to completed- Col. 13, line 55 change "such as E and F" to as close as E and F";

C01. 14, line 5 change "buss" to bus.

Signed and sealed this 27th day of June 1972.

SEAL) ttest:

EDWARD M.FLETCHER,JR. ROBERT GOTISCHALK Attesting Officer Commissioner of Patents F ORM PO-105O (10-69) USCOMM-DC 60376-1 69 u.s. GOVERNMENT PRINTING OFFICE: 1969 0-366-334 Patent No. 3,627,895 Dated December 14, 1971 Inventor(s) Peter T. Savon It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover page, correct the title to read --ELECTRONIC MUSICAL INSTRUMENT WITH DIRECT CURRENT KEYING OF PLURAL MUSICAL EFFECTS--;

Col. 5, line 72 change "B+" to --B- Col. 10, lines 21 and 22 delete "and their emitters biased through the resistor 30 to B potential";

Col. 11, line 29 change "B+" to --B- m;

C01. 12, line 63 change "complete" to completed-a;

Col. 13, line 55 change "such as E and F" to was close as E and F---;

Col. 14, line 5 change "buss" to bus- Signed and sealed this 27th day of June 1972.

SEAL) ttest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM po'loso (10459) USCOMM-DC scam-ps9 .5. GOVERNMENT PRINTING OFFlCEC 959 O 366-334 

1. An electronic musical instrument, comprising: a. a key-operated switch for being connected to a first source of DC-potential; b. an electronic gate having a control terminal; c. an inpUt resistor connecting said key-operated switch to said control terminal; d. a first and a second biasing resistor connected in series with each other and for being connected between a second source of DC-potential and the end of said input resistor more remote from said key-operated switch; e. a tab switch for being connected between a third source of DC-potential and a point between said first and second biasing resistors, said third source of DC-potential being of a level intermediate that of said first and second sources of DCpotential; f. a source of AC-potential of audio frequency having one extreme peak value corresponding to said third source of DCpotential; and g. means for converting electrical audio signals into sound and connected by said electronic gate to said source of ACpotential; h. said electronic gate being oriented to conduct current when a potential having a polarity opposite to that of said one extreme peak value is applied thereto.
 2. An electronic musical instrument according to claim 1, including: a. a pulse generator connected to be activated in response to closing of said key-operated switch; and b. means including a second tab switch for connecting said pulse generator to said point between said first and second resistors.
 3. An electronic musical instrument according to claim 2, including: a. a further input resistor, a further first and second biasing resistor, a further source of AC-potential and a further electronic gate, all connected to said key-operated key switch as set forth in claim 1; b. means including a third tab switch for connecting said pulse generator to said point between said further first and second resistors; and c. a percussive control tab switch connected to control the effectiveness of said second and third tab switches.
 4. An electronic musical instrument according to claim 1 including presetting means connected in electrical parallel with said tab switch for selectively providing a lesser potential to said point.
 5. An electronic musical instrument according to claim 4, including: a. a further input resistor, a further first and second biasing resistor, a further tab switch, a further source of AC-potential, a further electronic gate, and a further presetting means, all as set forth in claims 1 and 4; and b. a switch connecting both of said presetting means to said third source of potential.
 6. An electronic musical instrument according to claim 1, including: a further key-operated switch, a further input resistor, a further first and second biasing resistor, and a further tab switch, all connected as set forth in claim 1, whereby when said source of AC-potential is simultaneously gated by parallel paths, each including one of said key-operated switches and one of said input resistors, the amplitude of potential reaching said converting means will be increased.
 7. An electronic musical instrument according to claim 1, including: a. a pulse generator connected to be activated in response to closing of said key-operated switch, said generator being of the type operative to provide a train of pulses; and b. means including a second tab switch for connecting said pulse generator to said point between said first and second resistors.
 8. An electronic musical instrument according to claim 1, including: a. n- 1 further input resistors, n- 1 additional first and second biasing resistors, n- 1 further sources of AC-potential and n- 1 further electronic gates, all connected as set forth in claim 1; b. a pulse generator connected to be activated in response to closing of said key-operated switch, said generator having n outputs where n is at least 2, said generator being of the type operative to provide a series of pulses to each output and the pulses of each series being spaced in time from the pulses of the other series; and c. means including furTher tab switches for connecting the outputs of said pulse generator to said points between said n pairs of first and second resistors.
 9. An electronic musical instrument according to claim 1, in which said tab switch is a presetting means having impedance means for providing a potential at said point which is less than that of said third source of DC-potential.
 10. An electronic musical instrument comprising: a. a series of sources of AC-potential signals of audio frequency; b. a plurality of voicing circuits for shaping said audio signals; c. means connected to said voicing circuits for converting said audio signals to sound; d. a matrix assembly for keying said sources and thereby coupling them to said voicing circuits; e. a series of key switches connected to control said matrix assembly; f. a series of tab switches connected to said matrix assembly for connecting certain of said sources to certain of said voicing circuits; and g. a repeat circuit connected to said matrix assembly for periodically interrupting the connection from said key switches to said matrix assembly.
 11. An electronic musical instrument according to claim 10 including switching means for controlling said repeat circuit and including a separate switch for each of certain of said tab switches.
 12. An electronic musical instrument according to claim 11 in which there is one such separate switch for each of said tab switches associated with the various frequency ranges of one voice, the voicing circuits of other voices being unaffected by said repeat circuit.
 13. An electronic musical instrument according to claim 10 including a series of sustain keying circuits respectively connected between each of said key switches and said matrix assembly for providing repetition of tone signals during the decay produced by said sustain circuits.
 14. An electronic musical instrument according to claim 10 in which said repeat circuit includes a pulse generator having n phases providing a plurality of n trains of pulses, the pulses of each train being out-of-phase with each other train, and each train being connected to control the repetition of 1/n of said sources.
 15. An electronic musical instrument according to claim 14 including means responsive to the actuation of said key switches and connected to said pulse generator for simultaneously activating said n phases once after which said phases resume said out-of-phase operation.
 16. An electronic musical instrument according to claim 14, including: a. n means connected to the outputs of said pulse generator for respectively shaping the pulses of each train of pulses; and b. a single means connected to each of said shaping means for simultaneously controlling the shaping means to determine the envelopes of their output wave forms.
 17. An electronic musical instrument according to claim 10, including a percussion circuit connected to said matrix assembly and responsive to said key switches for controlling a selected portion of said matrix assembly to provide a control signal having a percussive envelope.
 18. An electronic musical instrument according to claim 17, including switching means for controlling said repeat and percussion circuits and including a separate switch for each of certain of said tab switches.
 19. An electronic musical instrument according to claim 10, in which said tab switches include a presetting means having impedance means for providing a reduced potential at said matrix assembly.
 20. An electronic musical instrument comprising: a. a series of sources of AC-potential signals of audio frequency; b. a plurality of voicing circuits for shaping said audio signals; c. means connected to said voicing circuits for converting said audio signals to sound; d. a matrix assembly for keying said sources and thereby coupling them to said voicing circuits; e. a series of key switches connected to contrOl said matrix assembly; f. a series of tab switches connected to said matrix assembly for connecting certain of said sources to certain of said voicing circuits; and g. a percussion circuit connected to said matrix assembly and responsive to said key switches for controlling a selected portion of said matrix assembly to provide a control signal having a percussive envelope.
 21. An electronic musical instrument according to claim 20, said percussion circuit having a single detector responsive to all of said key switches.
 22. An electronic musical instrument according to claim 20, said percussion circuit having switching means for controlling said percussion circuit and including a separate switch for each of certain of said tab switches.
 23. An electric musical instrument according to claim 22 in which there is one such separate switch for each of said tab switches associated with the various frequency ranges of one voice, the voicing circuits of other voices being unaffected by said percussion circuit.
 24. An electronic musical instrument according to claim 20 in which said percussion circuit includes a pulse generator having n phases providing a plurality of n trains of pulses, the pulses of each train being out-of-phase with each other train, and each train being connected to provide a percussive envelope for the control of a predetermined portion of said matrix.
 25. An electronic musical instrument according to claim 24, including means responsive to the actuation of said key switches and connected to said pulse generator for simultaneously activating said n phases once after which said phases resume said out-of-phase operation.
 26. An electronic musical instrument according to claim 24, including: a. n means connected to the outputs of said pulse generator for respectively shaping the pulses of each train of pulses; and b. a single means connected to each of said shaping means for simultaneously controlling the shaping means to determine the envelopes of their output wave forms.
 27. An electronic musical instrument according to claim 20, in which said tab switches include a presetting means having impedance means for providing a reduced potential at said matrix assembly.
 28. An electronic musical instrument according to claim 20, having switching means connected to and controlled by said percussion circuit and forming a part of the connection to said matrix assembly, said switching means enabling said percussion circuit to disable certain of the connections between said tab switches and said matrix assembly during operation of said percussion circuit.
 29. An electrical musical instrument according to claim 28, having a series of presetting means connected in electrical parallel to said tab switches and disabled by said switching means along with said certain of the connections to the matrix assembly.
 30. An electronic musical instrument according to claim 20 in which corresponding elements of said key switches are electrically common, means connected to said electrically common elements for selectably providing one of a plurality of potentials thereto for controlling the rate of attack of the keyed tone signals, and a switch forming a part of the connection between the percussion circuit and said matrix assembly and being further operative to apply a potential to said electrically common elements which effects a desired rate of attack.
 31. An electronic musical instrument according to claim 20 in which said percussion circuit has a plurality of separate switches for each of a plurality of tab switches, and a further master tab switch for controlling said percussion circuit.
 32. A sustain keying circuit for an electronic musical instrument comprising: a. a Darlington transistor having a collector connected to a source of keying potential, a base connected to be normally biased to be nonconductive, an emitter connected to an output terminal; b. capacitance means connected to said base and normally charged with the bias on said base; c. an input terminal for receiving a keying potential and connected to said base and capacitance means for reversely charging said capacitance means and rendering said Darlington transistor conductive; d. discharge circuit means connected to said capacitance means for effecting delayed discharge of said capacitance means in response to removal of said keying potential for maintaining a progressively decreasing bias potential on said base, and for thereafter providing the normal bias on said base; and e. means connected to the base of said Darlington transistor and responsive to the initial buildup of potentials in said circuit for dissipating any bias potential that would render said Darlington transistor conductive before its normal bias is applied.
 33. An electronic musical instrument, comprising: a. a source of DC-keying potential; b. a source of AC-potential of audio frequency; c. means for converting an electrical audio signal into sound; d. means connecting said source of AC-potential to said converting means and including a first electronic gate; e. means connecting said source of DC-keying potential to said first electronic gate, and including a second electronic gate; f. said second-named connecting means including a key switch connected to said source of DC-keying potential, and a sustain circuit directly connected to said key switch, responsive to the closing thereof, and forming part of the connection to said second electronic gate; and g. a tab switch connected to control said second electronic gate.
 34. An electronic musical instrument according to claim 33, in which said sustain circuit includes: a. a Darlington transistor having a collector connected to the source of keying potential, a base connected to be normally biased to be nonconductive, and an emitter connected to said second electronic gate; b. capacitance means connected to said base and normally charged with the bias on said base; c. an input means connected between said key switch and said base, for reversely charging said capacitance means for rendering said Darlington transistor conductive; and d. discharge circuit means connected to said capacitance means for effecting delayed discharge of said capacitance means in response to opening of said key switch for maintaining a progressively decreasing bias potential on said base, and for thereafter providing the normal bias on said base.
 35. An electronic musical instrument according to claim 34, including: a. an input resistor connected between the emitter of said Darlington transistor and said second electronic gate; and b. a biasing resistor connected between said tab switch and said second electronic gate. 